Personal tracked vehicles allow their users, and in some cases a passenger, to travel over rough (and in many cases unimproved) terrain. The best known example of a personal tracked vehicle is a snowmobile. Other types include all-terrain vehicles outfitted with (usually four) tracks instead of wheels and stand-up personal tracked vehicles (such as the one shown in U.S. Pat. No. 7,575,075).
Most convention personal tracked vehicles include a suspension system (or suspension systems) associated with their track or tracks. The suspension systems are designed to absorb at least some of the shocks produced by the vehicle traveling over the irregularities in the terrain. As the vehicle travels over the terrain, the irregularities produce displacements and deflections in its suspension system.
Given the length of time that snowmobiles have been in existence, probably the most advanced suspensions systems in these types of vehicles are found on snowmobiles. In a snowmobile, it is the rear suspension system that supports (in all mass-produced vehicles) a single endless track used to propel the vehicle. The endless track is tensioned and encircles a pair of parallel slide rails, a plurality of idler wheels and at least one drive wheel or sprocket. A shock absorbing mechanism involving compression springs, hydraulic dampers, and/or other shock absorbing elements urges the slide rails and the chassis (also known as a frame) of the snowmobile apart, against the weight supported above the suspension, in a static condition. The snowmobile suspension typically is a four bar linkage. These are only the generally characteristics of a modern snowmobile rear suspension. As those skilled in the art know, there are many detailed differences between the various conventional rear snowmobile suspension systems.
Owing to differences in their construction, other kinds of personal tracked vehicles do not use the same types of suspensions systems to support their tracks as do snowmobiles. Snowmobile rear suspensions are not directly applicable on these vehicles. The conversion kits used to convert standard 4-wheeled ATVs into 4-tracked vehicles (with one track replacing each wheel), typically use the suspension system already on the ATV (used with the wheel) alone, but in some cases do add components to such systems. In any event, they are different than snowmobile track suspension systems.
Different from either are stand-up personal tracked vehicles. Stand-up personal tracked vehicles are the most recent additional to this class of vehicles. As was discussed above, an example of such vehicle is disclosed in U.S. Pat. No. 7,575,075, issued to Fairhead on Aug. 18, 2009, incorporated by reference herein in its entirety. In such a vehicle, there is no seat. There is merely a platform on which the rider stands when using the vehicle. A pair of tracks (one on each side of the vehicle, below the platform) propels the vehicle. The engine is disposed below the platform laterally between the tracks. The user initiates vehicle turns by shifting their weight toward the right or the left, which causes one track to be driven faster than the other. Stand-up tracked vehicles are lighter, smaller and far more compact than snowmobiles and ATVs. For reasons including these, suspension systems similar to the ones used in snowmobiles or ATVs are not appropriate to such vehicles.
While the vehicle of the '075 U.S. patent did have an adequate suspension system, as is typically the case with these types of vehicles (see snowmobiles for example), improvements in suspension systems are always possible.